Lithography which uses an extreme ultraviolet light source for the microfabrication of next-generation semiconductors is anticipated. Lithography is a technique which reduces and projects light or beams onto a silicon substrate through a mask having a circuit pattern drawn thereon and forms an electronic circuit by exposing a resist material. The minimal processing dimensions of the circuit formed by optical lithography are basically dependent on the wavelength of the light source. Accordingly, the wavelength of the light source used for the development of next-generation semiconductors needs to be shortened, and thus a study for the development of such a light source has been conducted.
Extreme ultraviolet (EUV) is most anticipated as the next-generation lithography light source and the light has a wavelength in the range of approximately 1 to 100 nm. Since the light of the range has high absorptivity with respect to all materials and a transmissive optical system such as a lens may not be used, a reflective optical system is used. Further, it is very difficult to develop the optical system of the EUV light range, and only a restricted wavelength exhibits reflection characteristics.
Currently, a Mo/Si multilayer film reflection mirror with sensitivity of 13.5 nm has been developed. Then, lithography techniques obtained by the combination of the light of the wavelength and the reflection mirror is developed, it is expected that 30 nm or less of a processing dimension may be realized. In order to realize a new microfabrication technique, there is an immediate need for the development of a lithography light source with a wavelength of 13.5 nm, and radiant light from plasma with high energy density has gained attention.
The generation of light source plasma may be largely classified into laser produced plasma (LPP) using the radiation of laser and discharge produced plasma (DPP) driven by the pulse power technique.
The invention relates to an LPP EUV light source. The LPP EUV light source is disclosed in, for example, Patent Documents 1 and 2.
FIG. 1 is a diagram illustrating the structure of an LPP EUV light source of the related art disclosed in Patent Document 1. In this method, at least one target 57 is produced inside a chamber, and at least one pulse laser beam 53 is collected to the target 57 inside the chamber. The target is produced in the form of a jet flow of a liquid, and the laser beam 53 is collected to a portion where the jet flow is continuous in space.
Further, this device includes means for generating at least one laser beam 53, a chamber, means 50 for producing at least one target 57 inside the chamber, and means 54 for collecting the laser beam 53 to the target 57 inside the chamber. The target generating means 50 is configured to produce a jet flow of a liquid, and the collecting means 54 is configured to collect the laser beam 53 to a portion where the jet flow is continuous in space.
Furthermore, in this drawing, the reference numeral 51 indicates a light collecting point, the reference numeral 52 indicates a liquid droplet, and the reference numeral 55 indicates a liquid droplet formation point.
FIG. 2 is a diagram illustrating the structure of an LPP EUV light source of the related art disclosed in Patent Document 2.
This device includes a laser oscillating unit 61, a light collecting optical system 62 such as a light collecting lens, a target supply device 63, a target nozzle 64, and a EUV light collecting mirror 65. The laser oscillating unit 61 is a laser beam source that pulse-oscillates a laser beam which is used to excite the target substance. The laser beam emitted from the laser oscillating unit 61 is collected to a predetermined position by the light collecting lens 62. On the other hand, the target supply device 63 supplies the target substance to the target nozzle 64, and the target nozzle 64 injects the supplied target substance to a predetermined position.
When the target substance is irradiated with the laser beam, the target substance is excited to thereby produce plasma 66, and EUV light 67 (EUV) is emitted therefrom. The reflection surface of the EUV light collecting mirror 65 is provided with, for example, a film (Mo/Si multilayer film) which is formed by alternately stacking molybdenum and silicon in order to selectively reflect the EUV light with a wavelength near 13.5 nm. The EUV light 67 emitted from the plasma 66 is collected and reflected by the EUV light collecting mirror 65, and is output to an exposure apparatus in the form of output EUV light.